Removal of sulfur compounds from hydrocarbon fractions



July 22, 1952 J. E. coNNoR ET Al. 2,604,437

REMOVAL OF' SULFUR COMPOUNDS FROM HYDROCARBON FRACTIONS Filed April 23. 1949 235W), 7 mw Clbborne Patented July 22, 1952 John E. Connor and Clifford E; Gustafson,y Elizabeth, N. J assignors to Standard Oil `Development Company, a corporation -of Delaware Application April' 23', 1949', Serial o; 89,312'

The present invention is concerned with theremoval of sulfur compounds particularly mercaptan constituents from hydrocarbonv fractions. The invention is more particularly concerned with the removal Yof these-sulfur compounds froml hydrocarbonn fractions which boilY in thel motor fuel boiling range. In accordance with the'vpresent'invention these undesirable sulfur'constituents are'removed from hydrocarbon fractionsb'y treatingthesame with arr-alkali hydroxide solution which contains dissolved-therein a quantity'-A offelementary sulfur. In accordance with the preferred adaptation of the-presentinvention 'the' sulfur is dissolved in theA alkalihydroxidesolution at an elevated temperature; 'Ifhisis preferably accomplishedvby adding sulfur to a relatively con-` centrate'd alkali hydroxide solution followed by di1uting--theV same to a preferredtreatingconcen;

- tration,

Itis welll known in the art `toy treat petroleum oils byv #various-'procedures"in'order to `remove' ob= jectionable compounds, asfor; example sulfur compounds'therefrom. ForI example, it is'known totrea-t'petroleum fractions boiling in the `motor fuel boiling-range and inthe 'general' range [b'e lowabout 700 F, with variousichein'ical reagents such as, sodium` orpotassii'xin,v hydroxide so'lur tions. Also; it'has long Abeen known that weakly acidic materials, such as mercaptans; are reac- Y tive to various degrees with basic materials.` One method for-the removal of mercaptan compounds from hydrocarbon streams containing the-same has been to treatvthesestreams with a reagent which is insoluble in the hydrocarbon stream but which contains alkali typeiof Amaterial which reactsv with the mercaptan constituents.` Such treating agents have norma'll'ybeenaqueous-.soH

ylutions .of anv alkali material. The reaction product betWeenthe treating solution and the mercaptanrisabasic salt iof the mercaptan.` Normally. such salts exhibit some. solubility the aque.- Y ousphase. However, this solubilityv decreases ,as

the molecular. weight or.- branchiness of ,the hydrocarbon structure of the mercaptan increases.`

Therefore, caustic solutions when they'a're only spent to a small extent in mercaptide-saltsnwill not giveany further. reduction in, mercaptancon.-

tent .despite the fact that :these treating. solutionsI have a large residual free caustic content.- The* 'z claims'. (Cl. 19e-32):

art has also recognized thatithe efficiency of the` spent caustic can be partiallyor. fully restoredby regeneration of these solutions.V Theregeneration normally consists of removal of a part or` all of the mercap'tide'A salts-bymean'srof hydrolysis' and vaporization or by oxidation. 1

Onemetho'd is toemploy steam regenerationu for the revivication of causticrsolution spent in merca'ptanA removal fromV hydrocarbon` streanis The steam regeneration is normally carred'out" in a--packed towerior a tower provided with bubble i The plates 'Vor pierced type tray 'platedesign. steam hydrolize's the mercaptide salts to the' corresponding mercaptans which are stripped out byifthe steam vapors Vand taken overhead. The

regenerator also serves as raf means of adjustingk the." gravity df the caustic, solution! which has been. shownv to becritical. vTheregenerated caus- 'tic is Withdrawn'fr'omthe bottom ofthe regeneration.V tower and reused in the extraction stageof the systemwherein the caustic contacts the hydrocarbonfstream through suitable. mixing devices vfor-further:extraction of mercaptans by the same caustim Y l Thus; itis-apparent that sodiumhydroxideiper i seis not entirely satisfactory forthe removal cfg objectionable mercaptan constituentsffrom hy. brrrdrocarloon fractions containing thefs'amef It has rnovv been discovered however that providingthe alkali hydroxidesolution isgpretreatedl in a man;`

ner to dissolve sulfur, therein,- unexpectedv and desirable results are secured withrespect tothe* The pres@ removal of mercaptan constituents.

" `ent invention lmay be readily understood by reference vto the-drawings illustrating embodiments' of 'the' same-g Figure l'illustrates anadaptation of theV invention wherein. sulfur is added tothe alkali` hydroxide `solution vand thesame then heati ed to va temperature` Within .a critia1 range. 'Figarure f2, illustratesqan adaptation o f the invention s.. wherein the-heating ivssecuredV by dilution of a relatively concentrated alkali hydroxide solution.

Referring specically to Figure 1, a feed stream" which for` theepurpose. of illustration is assumed to'Y b'e ahy'drcarbon fra'ction'boilingin the "range belowf about 4:20". lli'sv introducedy into a depro paniz'ing -zone Ii by ymeans' ofline' ,Temperature,y and pressure conditionsaareadjusted? invzone fl., to remove overhead by meansfof line 3 a" strea'rly 3 comprising propane and lower boiling constituents. Hydrocarbon fractions boiling above the boiling range of propane is removed from the bottom of zone I by means of line 4 and introduced into a debutanization zone 5. A stream comprising butane is removed overhead from Zone 5 by means of line 6 while a stream substantially free of constituents boiling below the boiling range of butane is removed from the bottom of zone 5 by means of line 1. Y

This stream is introduced into zone 8 wherein it is contacted with an alkali hydroxide solution which is introduced into zone 8 by means of line 9 and withdrawn by means of line I0. The treated oil is withdrawn from zone 8 by means of line I I and introduced into zone I2 wherein the same is contacted with Va doctor solution 1 which is introduced by means of line I3 and withdrawn by means of line H5'. The doctor treated oil is' withdrawn from zone I2 by means ofgline I5 and introduced into water washing zone- I6 wherein it is contacted with water which is introduced by means of line I and withdrawn by means of line I8. The finished oil product is withdrawn from zone I5 by means of line I9 and further handled as desired. It is to be understood that zones I,

5,38, I2 and I6 may comprise any suitable numberV and arrangement of stages. Y

- In accordance with the present invention theV alkali hydroxide solution vemployed in zone `8, which for the purpose of illustration is assumed to be a sodium hydroxide solution, is prepared by introducing the sodium hydroxide solution into zone by means of line 2 I. Sulfur is introduced into zone 20by means of line 22. Suitable mixing devices may be employed. The stream iswith-l drawn from zone 20 by meansof line23 and introducedinto heating zone 24 wherein the same is heated to a temperature in the' range from about 150 F. to 190 F. The sodium hydroxide solution containing the dissolved sulfur is then' used` as described to treat the Anaphtha in zone 8. Referring specifically `to Figure' 2 it is assumed for the purpose ofillustration that theV operation Yis conducted as described with respect Vtol-ligure l,

persed throughout its volume is withdrawn fromV zone by means ofline 33 and mixed ,with water whichy is introduced by means V'of line 34. Iny

accordance with the preferred adaptation, the mixture Vis secured by passing the samev through a mixing device 36.v Due to the/dilution.effect,`

the-temperature of the sodium hydroxide solution is raisedA to a temperature within the range from about 150 Fgto 190 F., thus, securing the dis'-y solving of the sulfur in the sodium hydroxide. If necessary the temperaturemay be adjustedl to within this range by means'of heating-cooling zone 35. This sodium hydroxide solution containing `the dissolvedv sulfur is introduced-into niircaptans are first converted to oil soluble lead mercapes. solution." i. e., lead oxide dissolved in an aqueous caustic soda solution. The naphtha containing the lead mercaptan-hasV injected into it a sulfur solution 'the result being the conversion of the mercaptidesto a disulfide. and the formation of insoluble lead sulde. v g v Sulfur is added to zone L This is effected by contacting the oil with' doctor zone 8 by means of line 9 in an operation such as described in Figure 1. It is to be understood that the sulfurized sodium hydroxide solution need Vnot be hot when used to treat the oil stream in zone 8.

The present invention is broadly concerned with the use of a sulfurized alkali hydroxide solution for the removal of mercaptan constituents from hydrocarbon fractions containing the same. The invention is particularly adapted for the treatment of hydrocarbon fractions boiling below about 7 00 F. especially those fractions boiling in the motor fuel boiling` range (80.F,5420 F.). Especially desirable feedstocks for which the present invention is adapted are those fractions f which boil in the range from about 250 F. to

420 F. It is within this range that conventional alkali hydroxide solutions as for example sodium hydroxide solutions are not particularly .20

eiective in removing mercaptan constituents.

The alkali hydroxide solution may be any suit- .able solution, as for example, sodium or potassium'hydroxide. alkaline earth metal hydroxide solutions are satis- In general, the alkali and the factory.'v These metals among others comprise sodium, potassium, lithium, rubidium and cesium. The amount of sulfur used in conjunction with the alkali may vary appreciably. However, it is preferred that the amount be from Y5 to 10 parts ofA dry alkali by weight per 1 part of sulfur. If too little sulfur is used, satisfactory removal of the mercaptans is not secured, whereas, on the other hand if too much sulfur bel employed based upon the dry metal hydroxide, the mercury number1 of theV treated oil will increase prohibitively. The. concentration ofthe soda ern- 1 .Doctor sweetening process.-In this process the ployed in the treatment of thefeed oilsshould preferably be above 10 B. It is desirable that the concentration of the fresh soda should be in the range from 14 to 16 B.

i As pointed out heretofore, itis necessary thatv the alkali metal hydroxide solution containing the.

sulfurbe heatedl to a temperature in the range from about F. to 190 F. Whilevthis may be done by adding sulfur to a 14 to 16 B. soda solution and heating the same to a temperature with# in this range, a particularly desirable method in accordance with the present invention is to add sulfur to an alkali metal hydroxide solution hav-.1 ing a concentration inthe .rangefrom about`30f to` 35 B., and to dilute this solution to a .con-

centration inthe range from about 14 to 16 B. Under these conditions the temperature of the diluted solution will increase to within the desired temperature. range.`

The present invention may be more readilyune derstood by the followingexamples illustrating the'same. Y l

' EXAMPLE 1Y A 15 B. sodium hydroxide solution was mixed. with sulfur in the amount of one part of sulfur by-` weight basedA upon 10 parts of dry soda by weight; This Vsul'furized sodium hydroxide solution was used to treat a hydrocarbon fraction boiling in the solution'l containing no sulfur.

'1 Test'to'determine reactive sulfur present in sweetened stock. ',(Mercuryy number` is. equivalent to the mg. gof.

reactive sulfur per 1.100 ce.)4v Y f aie-04ans? Numbers Octane Untreated Feed Pass.

.en moro @s I Corrosion test.-This consists in immersing a bright copper strip for 3 Y 1 e` oil maintained at 212 l. to determine -fthepresence o "corrosiveUsulfnr inthe oil asv indicated-by discoloration and pitting of the copper. y Y 1 Breakdown' introduction' tor u 2#drop. v25'cc. 0I oil a pcrtiireof 2l2F. under .oxygen pressure 01'100# per sqy From thef-aboveit-fls readily fapparent f-thatlthe use of su-lfurizedsediumdydroxide produces :f a treateu'di stok of considerabl that sec'rird-whentreati'ngt thfan unsulfu ized sodiumhydroxidesolutien. 1- i Y EXAMPLE 2 A prime cut naphtha having a copper number of 37 was treated with a sodium hydroxide solution (15 B.) to which was added one gram of sulfur per grams of dry sodium hydroxide. Another portion of the prime cut naphtha (80 to 420 F.) was treated with a soda solution (15 B.)

A debutanized feed naphtha having a copper number of 331/2 was treated with a 15 B. soda solution preparedV in accordance with the present invention and with a soda solution which did notcontain any added sulfur. After treatment with the soda the naphtha was doctor sweetened. The results of these operations are as follows:

Copper Mercury No. No.

Debutanizer Bottoms. 33% After Be. soda-i-sulf 8 it After 15 B. soda 16 1 EXAMPLE 4 A debutanized naphtha was treated with a 15 B. caustic solution. Other portions were treated with a 15 B. caustic solution containing sulfur in accordance with the present invention. The respective caustic solutions were withdrawn from the treated naphtha and reused on fresh naphtha. The copper number of the respective treated naphthas were determined with the following resuits.

Copper No. 34- Soda-l-sulur used Debutanizer Bottoms- Soda used One treat 16 One treat 8 Two treats... 23 Two treats.- 9 Three treats. 26 10 Four treats 31 .Mffrber Where it is described hou sped-in a bombtalteuri- *The time inmin'utess measuredduring which the pressuredrops 2#and takenas 4hebrealulown.

ieper quautyitnan zItis apparentthatjnotonlyiis provementisecuredfin the removal-fth' f'captanswvh'en us'i'ng :the 'sulfurize'd i1 caust'i tion, but also that the solution can be reus'd with marked 'effectv over an unsul'f-urize'd eausticisolution. The above data'shows for example that when the sulfurized caustic solution is used the third time, the treated naphtha had a copper number of 10, whereas, when the unsulfurized caustic solution was used a third time the naphtha had a copper number of 26.

Thesey naphthas were subsequently doctor sweetened to a copper number less than one-half. The amount of doctor solution required with respect to the above series of treatments is as follows:

Soda used When using Sulurlzed Soda using non-sulfurized' soda. Y,

of amount used when' yAs pointed out heretofore, the concentration of the caustic used is preferably in the range from about 14 to 16 Be. The quantity employed may vary appreciably, but in general it is preferred to use from about 10 to 30% by volume of caustic solution based upon the volume ofy oil being treated. With respect to the examples given, approximately 20% by volume of caustic was employed based upon the volume of oil treated.

Having described the invention it is claimed:

1. Improved process for the removal of mercaptan compounds from a hydrocarbon fraction containing the same which comprises adding sulfur to an aqueous alkali metal hydroxide solution, heating the same and thereafter contacting the hydrocarbon fraction with said aqueous alkali metal hydroxide solution, whereby said mercaptan compounds are removed from said hydrocarbon fraction.

2. The process as dened by claim 1 wherein said hydrocarbon fractions boils in the range from about 250 F. to 420 F. and wherein said alkali metal hydroxide solution comprises sodium hydroxide.

3. Process for the removal of mercaptan compounds from petroleum fractions boiling in the range from about F. to 420 F. which comprises adding sulfur to an aqueous metal hydroxide solution, heating the mixture to a temperature in the range from about to 190 F. and thereafter contacting said petroleum fractions wth said aqueous metal hydroxide solution whereby said mercaptan compounds are removed from said fractions. Y4. Process as defined by claim 3 wherein said alkali'metal hydroxide solution comprises a so-` dium hydroxide solution having a gravity in the range from about 14 B. to 16 B. and wherein the amount of sulfur added is in the range from about one part of sulfur by weight per 5 parts of dry caustic.

5. Process for the removal of mercaptan com# pounds from petroleum fraction boiling in the A range from about 80 F. to 420 F. which comprises adding sulfur to an aqueous alkali metal hydroxide solution having a gravity in the range from about 30 B. to 35 B., diluting said alkali metal hydroxide solution with water, whereby an elevated temperature is secured, allowing the diluted mixture to cool and then contacting said petroleum fraction with said diluted cooled alkali metal hydroxide solution whereby said mercaptanA compounds are removed from said petroleum fraction. y .y e

6. vProcess as defined by claim 5 wherein the 8 amount of sulfur added isv one part of sulfur by weight per 5 to 10 partsof dry caustic by weight. 7. Process as defined by `claim 6 wherein said alkali metal hydroxide solution comprises a sodium hydroxide solution.

JOHN E'. CONNOR. CLIFFORD E. GUSTAFSON.

REFERENCES CITED A l The following references are of' record in the Y 111e of this patent:

UNITED STATES PATENTS 

1. IMPROVED PROCESS FOR THE REMOVAL OF MERCAPTAN COMPOUUNDS FROM A HYDROCARBON FRACTION CONTAINING THE SAME WHICH COMPRISES ADDING SULFUR TO AN AQUEOUS ALKALI METAL HYDROXIDE SOLUTION. HEATING THE SAME AND THEREAFTER CONTACTING THE HYDROCARBON FRACTION WITH SAID AQUEOUS AKLALI METAL HYDROXIDE SOLUTION, WHEREBY SAID MERCAPTAN COMPOUNNDS ARE REMOVED FROM SAID HYDROCARBON FRACTION 